1. Field of the Invention
The present invention relates to improved intervertebral implants for spinal fusion.
2. Description of Related Art
Current spine procedures for treating damaged or diseased intervertebral discs are critically dependent upon achieving interbody fusion—the replacement of the diseased disc with a spacer that allows bone growth to fuse the adjacent vertebral bodies. Titanium cages or PEEK spacers containing autograft or allograft bone are currently utilized to achieve this medical outcome, but are frequently unsuccessful due to a poor rate of bone growth that fails to achieve complete fusion. A systematic review of the literature reveals that anterior interbody fusion rates vary from 47% to 90%, suggesting a less than excellent fusion rate with current technology. Titanium cages appear to provide insufficient lordotic angle and the fused area of local bone inside cages at regions exposed to endplates is insufficient for physiologic load transmission. PEEK devices appear to represent a reasonable alternative but a thick wall construct is required using PEEK to provide sufficient biomechanical strength during the fusion process. The volume of the solid PEEK insert cannot be replaced by bone, as this biomaterial is not degradable and remains within the body indefinitely. Thus, the overall volume of the new bony column is decreased, contributing to less stability and strength. Existing devices also suffer from problems of subsidence into the adjacent vertebral bodies over time.
Thus, there remains a need in the art for intervertebral implants that promote successful interbody fusion and avoid problems of subsidence seen in existing devices.